1. Field of the Invention
The present invention relates to an apparatus for positioning a printing plate to a plate cylinder of a printing machine and, more specifically, to a positioning apparatus for carrying out positioning of the printing plate to the plate cylinder by contacting a fore-end of the printing plate to a reference member provided on a clamping base of the plate cylinder.
2. Description of the Prior Art
FIG. 15 shows a sectional side elevation of a plate cylinder 45. The plate cylinder 45 is rotatably supported with a plate cylinder shaft 45J to a body of a printing machine. A printing plate 10 is disposed on an outer surface of the plate cylinder 45.
In order to dispose the plate 10 on the cylinder 45, the operator of the printing machine initially inserts a leading edge side part 10a of the plate 10 into a gap formed between a leading edge side clamping base 51 and a leading edge side clamp 52, then the leading edge side part 10a is clamped therebetween by closing the leading edge side clamp 52.
Next, the plate 10 is rolled around the outer surface of the cylinder 45, and then a tail edge side part 10b of the plate 10 is inserted between a tail edge side clamping base 53 and a tail edge side clamp 54. The tail edge side part 10b is clamped therebetween by closing the tail edge side clamp 54. Thereafter, the plate 10 is fitted tightly on the outer surface of the cylinder 45 by pulling the tail edge side part 10b as a result of moving both the tail edge side clamping base 53 and the tail edge side clamp 54.
In order to carry out appropriate printing work, the plate 10 needs to be disposed on the outer surface of the cylinder 45 with accuracy. To do that, cut-out parts 10S for positioning are formed at two separate positions on the leading edge side part 10a of the plate 10 as depicted in FIG. 14. Two separate positioning pins 11 responsive to the cut-out parts 10S are provided to the leading edge side clamping base 51 of the cylinder 45 in fixed manner as shown in FIG. 16.
Further, a temporal fixer 20 depicted in FIG. 16 is provided to the clamping base 51. The temporal fixer 20 is made of a thin metal plate and the fixer 20 is arranged such that a part adjacent to a fore-end thereof is in contact with an upper surface 51F of the clamping base 51.
The operator carries out positioning of the plate 10 accurately by contacting cut-out planes 13 of the cut-out parts 10S (FIG. 14) with the positioning pins 11 while inserting the leading edge side part 10a between the fixer 20 and the upper surface 51F with force when the leading edge side part 10a is inserted between the leading edge side clamping base 51 and the leading edge side clamp 52.
The fixer 20 has elasticity because it is made of a thin metal-plate. The elasticity thereof allows the fixer 20 to fix the leading edge side part 10a between the fixer 20 and the upper surface 51F under a temporarily basis. The leading edge side part 10a is clamped between the leading edge side clamping base 51 and the leading edge side clamp 52 by closing the leading edge side clamp 52 as a result of rotating a cam (not shown) with a spanner and/or similar tool(s) under the condition described above.
Another conventional apparatus for positioning a printing plate is disclosed in Japanese patent laid-open publication No. Hei 6-286112. The overall mechanisms of the apparatus are shown in FIG. 17. In the conventional apparatus, the leading edge side part 10a is inserted between the leading edge side clamping base 51 and the leading edge side clamp 52 as a result of suspending the printing plate 10 downwardly to the plate cylinder 45 with the apparatus.
A cylinder 26 is provided with to a safety cover 28 for a printing unit, and a pair of cover arms 23 are connected to the cylinder 26 through a link mechanism 27. A protection cover 22 is suspended and held by the cover arms 23. A shaft 24 is provided to the cover arms 23 so as to cross therebetween, and a stopper 21 is provided on the shaft 24.
In the normal state, the protection cover 22 is positioned adjacent to the safety cover 28. The protection cover 22 is moved to the position shown in FIG. 17 by actuating the cylinder 26. Thereafter, the leading edge side part 10a is inserted between the leading edge side clamping base 51 and the leading edge side clamp 52 while contacting the tail edge side part 10b to the stopper 21. At that time, guide rollers 25 provided on the protection cover 22 support the printing plate 10. The leading edge side part 10a is clamped to the leading edge side clamping base 51 and the leading edge side clamp 52 is closed by closing the leading edge side clamp 52 under the condition depicted in FIG. 17.
The conventional apparatuses for positioning a printing plate, however, have the following problems to be solved. In order to dispose the plate 10 on the cylinder 45 at a proper position, the cut-out planes 13 of the cut-out parts 10S need to be accurately contacted with the positioning pins 11 provided to the leading edge side clamping base 51 as two separate pins.
The cut-out planes 13 possibly contact with the positioning pins 11 in insufficient ways because the leading edge side part 10a is inserted between the fixer 20 and the upper surface 51F with force. Uneven contact of the cut-out planes 13 to the positioning pins 11 makes diagonal placement of the printing plate 10 on the plate cylinder 45 possible. Consequently, printing accuracy may be decreased as a result of diagonal images caused by the diagonal placement.
There is a high probability to deform the cut-out planes 13 as a result of giving too much force thereto when the operator tries hard to contact the cut-out planes 13 with the positioning pins 11 sufficiently. Consequently, printing accuracy may also be decreased as a result of diagonal images caused by the deformation of the cut-out planes 13.
As described above, printing accuracy may be decreased as a result of difficulties of disposing the printing plate 10 on the cylinder 45 at a proper position when the apparatus depicted in FIG. 16 in which the leading edge side part 10a being fixed under a temporarily basis, is used. It requires the operator to be skillful in order to dispose the printing plate 10 at a proper position.
In the apparatus shown in FIG. 17, the leading edge side part 10a can not be inserted between the leading edge side clamping base 51 and the leading edge side clamp 52 with force because the leading edge side part 10a is inserted therebetween by its weight or flexure thereof. In this way, the apparatus employs a mechanism in which the cut-out planes 13 just contact with the positioning pins 11 while not employing the fixer 20 depicted in FIG. 16.
The printing plate 10 might be held under a condition that a part adjacent to the leading edge side part 10a comes up from the upper surface 51F of the clamping base 51. The leading edge side part 10a moves its position to an axis of the positioning pins 11 (vertical direction in FIG. 16) when the leading edge side clamp 52 is closed as a result of pushing force thereof. Consequently, printing accuracy may be decreased as a result of diagonal images caused by its diagonal placement.
In addition, the apparatus shown in FIG. 17 requires many parts such as the cylinder 26, the link mechanism 27, the cover arms 23, the protection cover 22, the guide rollers 25 and so on. Consequently, complex mechanisms are needed, and the printing plate 10 is supported in an unstable manner.